The present invention relates to methods and apparatus for producing uniform discharge and suction flow rates and, more particularly, to a hydraulically actuated uniform flow rate pumping system.
Such pumping systems can be used in moving heavy fluids, such as mud which must be removed during oil well drilling operations. Once pumping of a heavy fluid is initiated and a column of fluid is placed in motion by the pumping action, considerable momentum is created by the moving column of fluid. So as to minimize loss of energy, it is therefore desirable to impart a constant or uniform flow rate to the column of fluid, rather than a pulsating flow rate. A uniform flow rate also serves to reduce the occurrence of fatigue in the pipes and lines carrying the moving fluid, as compared with the amount of fatigue which results from the application and absorption of pulsed energy.
Known positive displacement pumps include the use of reciprocating pistons sliding back and forth within cylinders, or plungers sliding back and forth within stuffing boxes, thereby increasing and decreasing a working volume. Check valves control entry into and discharge from the working volume so as to create a pulsating flow by alternate sucking and discharging of the piston or plunger. In order to smooth the pulsating flow, two opposed stuffing boxes having a common piston therebetween have been used so as to produce a double acting pump. Further smoothing of the discharge flow may be accomplished by introducing short-time accumulators in the pipe lines so as to dampen the peaks and fill the valleys that occur during and after the pulsating flow, respectively. Alternately, a number of in-line cylinders each having a piston operated by a common drive may be employed, with each piston being located at a different displaced position within its cylinder relative to the other pistons and their cylinders, so that overlapping of the discharge strokes serves to smooth the total discharge flow.
In known systems employing these foregoing principles, the presence of a number of piston cylinders requires complicated gear reduction mechanisms. Furthermore, known systems for producing a smoothed flow rate utilize linear increases and decreases in the velocity of the pumping pistons, resulting in excessive piston jerk whenever the pistons change direction of movement. This produces fatigue in the piston and associated parts, thereby decreasing the effective life of such pumping systems.